Report calls to deprecated methods as errors in PHP log

This patch enables the '$wgDevelopmentWarnings' setting in LocalSettings.php.
With the setting enabled, calls methods that have been marked as deprecated
using 'wfDeprecated()' will be reported in the PHP error log with the error
code E_USER_DEPRECATED.

Change-Id: I1664f9b91b410c7421bef59db9ecc5b5165ac953
Merge "Report calls to deprecated methods as errors in PHP log"